I happened to see the Vidsonix drivers within hours of the post, and it seems like a good way to get there as well. Thinking in terms of actions and opposite reactions, I can only imagine that the inertia of the driver is what anchors it against the plate. I'm curious now if the anchoring of the driver to the frame really makes that much of a difference. There's that "ah gee, I didn't consider that" all over again. Then again, my idea using a modified PA driver requires a sturdy anchor in the first place.
In my mind, I always considered the frame of the plate reverb as part of the actual mechanism itself. That's why it always made sense to me to tie the housings of the moving parts (transducers) to the frame itself, even if it meant damping the frame from the rest of the world.
Solo harmonies and multiparts. Do THAT in a karaoke bar!